1. Field of the Invention
The present invention relates to a diode, which is one of semiconductor devices making up a high withstand voltage power module of 600 V or higher, and more particularly, to a semiconductor device capable of improving oscillation resistance or recovery resistance and suppressing a snap-off phenomenon, and a method for manufacturing the same.
2. Background Art
FIG. 30 is a diagram illustrating a relationship between an ON voltage VF and a recovery loss Erec of a diode. There is a trade-off relationship between the two. Arbitrary points on the trade-off curve are used depending on the product applied. To obtain a diode having characteristics at arbitrary points on the trade-off curve, lifetime has been conventionally controlled by controlling impurity concentration of a P-type anode layer or through electron beam radiation.
When a reverse bias is applied to a diode, a depletion layer extends toward both sides of the anode and cathode. When the impurity concentration of the P-type anode layer is lowered, the depletion layer is likely to extend toward the anode side when a high voltage is applied thereto, which causes a reach-through of the electric field on the anode side, resulting in a problem of leading to a drop in the withstand voltage. However, lowering the impurity concentration of the P-type anode layer makes it possible to reduce a reverse recovery current Irr during recovery operation and thereby reduce recovery loss. Thus, to reduce Irr, the impurity concentration of the P-type anode layer is conventionally reduced within a range in which the withstand voltage can be maintained and the lifetime is controlled to obtain arbitrary characteristics on the trade-off curve. Furthermore, a diode with a trench formed on the anode side has been proposed so far for the purpose of realizing low leakage current and low Irr (e.g., see Japanese Patent Laid-Open No. 11-97715).